(1) Field of the Invention
The present invention relates to a disc recording and/or playback apparatus, and more particularly to a disc recording and/or playback apparatus with an automatic changer capable of storing a plurality of discs, each of which may be contained within a cartridge but simply referred to as a "disc" even in that case hereinafter, and automatically selecting desired discs for sequential recording and/or playback operation.
(2) Description of the Prior Art
There have been developed various disc recording and/or playback apparatus with automatic changer devices for recording information on and/or playing back a plurality of discs in sequence. Basically, as shown in FIG. 1 of the accompanying drawings, such a disc recording and/or playback apparatus (simply referred to as a playback apparatus hereinafter) with automatic changer has a storage unit 2 for storing a plurality of discs 1 at a pitch P, two disc process means 3 each including a turntable and recording and/or pickup units, and a disk draw/feed mechanism (described later) for successively selecting desired discs from the storage unit 2 and feeding them, one at a time, onto the turntable, and for returning such discs, one at a time, from the disc process means into the storage unit 2. Each of the discs 1 is rotatably housed in a flat rectangular cartridge 4, and delivered onto the turntable for recording and/or playback while being housed in the cartridge 4. The two disc process means 3 are stacked one on the other below the storage unit 2. Each of the playback means 3 has a slot 3a defined in its housing for inserting a cartridge 4 with a disc 1 therein.
A guide shaft 5 extends along the array of the discs in the storage unit 2 in the direction of the arrow z, and a base 6 is slidably mounted on the guide shaft 5. A hollow rectangular rotatable body 7 is mounted on the base 6 by a spindle 8, the body 7 being rotatable about the spindle 8 in the direction of the arrow Q. Although not shown, the apparatus also includes a driving means for moving the base 6, and a rotating means for rotating the rotatable body 7. In the rotatable body 7, there are disposed gripper arms (not shown) for gripping each cartridge 4, the gripper arms being reciprocally movable in directions (the direction of the arrow X and the direction opposite thereto) normal to the direction in which the discs are arrayed. The apparatus also includes a gripping force imparting means (not shown) for imparting a gripping force to the gripper arms, and a driving means (not shown) for moving the gripper arms.
An address plate 10 is disposed alongside of the storage unit 2 and extends along the array of the discs. The address plate 10 has an absolute address slit group comprising a plurality of slits 10a positionally corresponding to the respective disc storage positions in the storage unit 2 in which the discs 1 are stored, respectively, and a positioning slit group comprising a plurality of slits 10b positionally corresponding to the respective discs 1 stored in the disc storage positions. To the base 6, there are attached a photosensor 11 for detecting the absolute address slit group and a photosensor 12 for detecting the positioning slit group.
When a disc to be played back is specified, the base 6 is moved to a position where the gripper arm can grip the cartridge 4 which stores the specified disc. At this time, the absolute address slit group and the photosensor 11 detect when the base 6 has arrived near that position, and the positioning slit group and the photosensor 12 detect when the base 6 is exactly positioned at that position.
In the disc playback apparatus shown in FIG. 1, when the rotatable body 7 is reversed or turned around for playing back both sides of the disc 1, the free end of the rotatable body 7 tends to be displaced by an offset .DELTA., as shown in FIG. 2, due for example to an error in parallelism between the rotatable body 7 and the spindle 8 and dimensional errors of various parts. The absolute address slit group and the positioning slit group, and the photosensors 11, 12 are relatively positioned such that the position of the rotatable body 7 with one side, e.g., "side A", of the disc 1 facing upwardly, i.e., the position of the rotatable body 7 indicated by the solid lines in FIG. 2 will be aligned with each cartridge storage position in the storage unit 2. Even with such a positional setting, however, if the offset or deviation .DELTA. is large, the cartridge 4 may not be transferred between the rotatable body 7 and the storage unit 2 when the rotatable body 7 is turned upside down for playing back the side B of the disc 1. Therefore, the dimensional and assembling accuracy of the parts of the mechanism for feeding the discs has to be high in the conventional disc playback apparatus in order to minimize the deviation .DELTA.. As a result, the conventional disc playback apparatus has been costly to manufacture.